1. Field of the Invention
The invention relates to a lens module and more particularly to a lens module with a voice coil motor for focusing.
2. Description of the Related Art
In various photographic apparatuses, a motor is usually used as an actuator to drive a lens for focusing. A voice coil motor (VCM) is a cheaper product on the market and is usually applied to photographic apparatuses, for example a cell phone which can takes photos. FIGS. 1-5 are schematic views of conventional lens modules. Shown in FIG. 1, the lens module sequentially includes a base 1, a second elastic sheet 2, an insulating sheet 3, a lens sleeve 4, a limiting assembly 5, a first elastic sheet 6, and an upper cover 7. The base 1 is connected to the upper cover 7 to form a space for accommodating other elements. The lens sleeve 4 is slidably installed in the space, and comprises a coil and a central hole for fixing the lens. The limiting assembly 5 is installed on the lens sleeve 4, and comprises a magnet therein. The coil respectively connects to opposite end portions of the second elastic sheet 2. The second elastic sheet 2 is respectively electrically connected to the positive and negative electrodes via wiring terminals 8 and 9. After electrifying, the electromagnetic force drives the lens sleeve 4 to link the lens to move upward and downward for focusing. The first elastic sheet 6 and the second elastic sheet 2 respectively generate opposing resistances for the lens sleeve 4 to balance the electromagnetic force.
During assembly, the coil of the lens sleeve 4 is connected to the second elastic sheet 2. Then, the base 1, the insulating sheet 3, the limiting cover 5, the first elastic sheet 6, and the upper cover 7 are sequentially assembled. Each element, especially the first elastic sheet 6 and the second elastic sheet 2, are fixed on different members. Thus, cumulative inaccuracies exist and coaxality is difficult. Additionally, the second elastic sheet 2 is engaged with the base 1. Thus, because the fixing method is unreliable, the second elastic sheet 2 easily rotates and deforms.
Referring to FIG. 2, to effectively fix the second elastic sheet 2, some lens modules comprise a plurality of fixing members 10 on an outer edge of the second elastic sheet 2. The base 1 comprises a plurality of holes 11. When the second elastic sheet 2 is assembled with the base 1, the holes 11 are filled with the adhesive, and then the fixing members 10 are inserted. Thus, the second elastic sheet 2 is connected to the base 1. Such connecting method is complex, drying time of the adhesive costs time, and assembly yield decreases.
Referring to FIG. 5, when the lens is assembled with a holder 15, the holder 15 rotates, thus decreasing assembly yield. Thus, the holder 15 comprises a plurality of radial protrusions 18 on the outer edge, and the base 17 comprises a plurality of grooves 19 on the inner edge corresponding to the radial protrusions 18 for ensuring that the holder is fixed during lens assembly. Such a structure prevents the holder 15 from rotating with the base 17. However, lens module volume increases for such a structure. Thus, miniaturization trends of cameras and cell phones with cameras are hindered.